Cellulose acetate and cellulose acetate composition

ABSTRACT

This cellulose acetate has a total degree of acetyl substitution of 1.75 or more and 2.55 or less, and a degree of acetyl substitution at 2-position or a degree of acetyl substitution at 3-position is 0.7 or less. This cellulose acetate composition includes the cellulose acetate and an additive. The additive is one or more selected from the group consisting of (a) substances of which a pH of a 1 wt. % aqueous solution at 20° C. is 8 or more, (b) substances that dissolve in water at 20° C. in an amount of 2 wt. % or more, and (c) substances that exhibit biodegradability in seawater.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.17/715,989, filed Apr. 8, 2022, which is a continuation of PCTInternational Application No. PCT/JP2020/039573 filed on Oct. 21, 2020,the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to cellulose acetate and a compositioncontaining cellulose acetate.

BACKGROUND ART

In recent years, there has been a demand for biodegradable moldedarticles due to growing interest in global environment. Examples ofrepresentative biodegradable resins include cellulose acetate.

For example, cellulose acetate having a degree of substitution of about2.5 is used as a material for a cigarette filter used in cigarettesincluding e-cigarettes, as a material for a sanitary article, or thelike. Cellulose acetate having a degree of substitution of about 2.5 isknown to decompose in soil or activated sludge. However, thebiodegradability thereof falls short of cellulose or cellulose acetatehaving a degree of substitution of 1.8.

From the viewpoint of improving the biodegradability, the degree ofsubstitution of cellulose acetate is preferably low, but a certaindegree of substitution of acetyl is required because of the ease ofprocessing by thermoforming or the like. Various studies have been madefor the purpose of improving the biodegradability and moldability.

Patent Document 1 discloses a technique for improving thebiodegradability of a polymer such as cellulose ester by adding a basicadditive having a pH of 13 or less and 7 or more in a 1% aqueoussolution (20° C.) in the polymer.

Patent Document 2 discloses a technique for reducing the viscosity of acellulose acylate solution used in the solvent casting method by setting−0.1≤(degree of acyl substitution at 3-position−degree of acylsubstitution at 2-position)≤0.3 in cellulose acylate having a totaldegree of acyl substitution of 2.67 or more at 2-, 3-, and 6-positions,and a total degree of acyl substitution of 1.97 or more at 2- and3-positions.

CITATION LIST Patent Document

Patent Document 1: JP 2018-500416 T

Patent Document 2: JP 2002-265501 A

SUMMARY OF INVENTION Technical Problem

As mentioned above, cellulose acetate is known to be decomposed in soilor activated sludge. However, there is a problem that a satisfactorydecomposition rate cannot be obtained in a water system having a smallernumber of bacteria than activated sludge, for example, in sea water.

An object of the present disclosure is to provide cellulose acetate anda composition that have excellent marine biodegradability.

Solution to Problem

As a result of intensive studies, the present inventors have found thatbiodegradability in the sea is remarkably improved even in celluloseacetate having a relatively high total degree of acetyl substitution byheterogeneously introducing acetyl groups into carbon atoms at 2-, 3-,and 6-positions of a glucose ring, and have completed the presentdisclosure.

That is, the cellulose acetate according to the present disclosure has atotal degree of acetyl substitution of 1.75 or more and 2.55 or less,and at least one of the degree of acetyl substitution at 2-position orthe degree of acetyl substitution at 3-position is 0.7 or less.

Preferably, in the cellulose acetate, the degree of acetyl substitutionat 2-position and the degree of acetyl substitution at 3-position eachare 0.7 or less.

Preferably, the cellulose acetate has a total degree of acetylsubstitution of 2.00 or more. Preferably, the cellulose acetate has atotal degree of acetyl substitution of 2.20 or less.

The cellulose acetate according to the present disclosure contains anyof the cellulose acetate described above and an additive. This additiveis selected from the group consisting of (a) substances of which a pH ofa 1 wt. % aqueous solution at 20° C. is 8 or more, (b) substances thatdissolve in water at 20° C. in an amount of 2 wt. % or more, and (c)substances that exhibit biodegradability in seawater.

Preferably, a content of cellulose acetate in the entire composition is50 wt. % or more. Preferably, a total content of additives in the entirecomposition is 3 wt. % or more and 40 wt. % or less.

Preferably, the substance (a) of which a pH of a 1 wt. % aqueoussolution at 20° C. is 8 or more is selected from the group consisting of(a1) to (a3) below:

(a1) inorganic compounds containing an oxygen atom bonded to any metalelement of Na, K, Ca, or Mg,

(a2) metal salts containing one or more metal ions selected from Na⁺,K⁺, Ca²⁺, or Mg²⁺, and one or more anions selected from a carbonate ion,a bicarbonate ion, a silicate ion, or an aluminate ion, and

(a3) inorganic compounds containing magnesium.

Preferably, the main component of the inorganic compound (a3) containingmagnesium is magnesium oxide.

Preferably, the substance (b) that dissolves in water at 20° C. in anamount of 2 wt. % or more is selected from the group consisting of (b1)to (b3) below:

(b1) glycerin esters,

(b2) citrates, and

(b3) polyethylene glycols having a number average degree ofpolymerization of 20 or less.

Preferably, the substance (c) that exhibits biodegradability in seawateris a polyester having a weight average molecular weight of 50,000 orless.

Preferably, the cellulose acetate composition contains an additiveincluding a combination of magnesium oxide and triacetin.

Advantageous Effects of Invention

The cellulose acetate and the cellulose acetate composition according tothe present disclosure are excellent in biodegradability, particularlybiodegradability in seawater.

DESCRIPTION OF EMBODIMENTS

The present disclosure is described in detail below based on preferableembodiments. The scope of the present disclosure is not limited to thesedescriptions, and can be appropriately changed and implemented within arange not impairing the gist of the present disclosure, in addition tothe following examples. In addition, the present disclosure is notlimited to the following embodiments, and various modifications can bemade within the scope described in claims. Other embodiments obtained byappropriately combining the technical means disclosed for each of theplurality of embodiments are also included in the technical scope of thepresent disclosure.

In the present specification, “X to Y” indicating a range means “X ormore and Y or less”. Also, unless otherwise noted, “ppm” means “ppm byweight”.

[Cellulose Acetate]

The cellulose acetate of the present disclosure has a total degree ofacetyl substitution (DS) of 1.75 or more and 2.55 or less, and at leastone of the degree of acetyl substitution at 2-position (DS2) or thedegree of acetyl substitution at 3-position (DS3) is 0.7 or less. Thiscellulose acetate is excellent in biodegradability, particularlybiodegradability in seawater.

The mechanism of biodegradation of cellulose acetate will be describedbelow. The biodegradation of cellulose acetate is believed to progressunder an action of an enzyme (for example, β-glucosidase; EC 3.2.1.21)that decomposes cellulose after each acetyl group of cellulose acetateis hydrolyzed to reduce the degree of substitution. β-glucosidase is anenzyme that catalyzes the hydrolysis reaction of β-glycoside bonds ofsugars. β-glucosidase is also called β-D-glucoside glucohydrolase andamygdalase. When the β-glycoside bond constituting a polymer chain ofcellulose acetate is hydrolyzed, a monosaccharide or a low molecularweight polysaccharide is obtained. The monosaccharide or the lowmolecular weight polysaccharide is decomposed by normal microbialmetabolism. Therefore, in order to promote biodegradation of celluloseacetate, it is effective to promote elimination of an acetyl group.

In the related art, cellulose acetate having a low degree ofsubstitution of acetyl groups is considered to have excellentbiodegradability from this consideration. This consideration is notwrong. However, when the degree of substitution is low, the meltviscosity increases, and thermal decomposition easily occurs. As aresult, the thermoforming of cellulose acetate having a low degree ofsubstitution is difficult.

Meanwhile, hemicellulose constituting wood contains an acetyl group inpart. It is known that this acetyl group is bonded to xylan to formacetylxylan in hardwoods. This acetylxylan is also biodegradable. It isknown that acetylxylan esterase (EC 3.1.1.72) exists in order todecompose acetylxylan and the like. The acetylxylan esterase is anenzyme that catalyzes deacetylation of xylan and xylooligosaccharide.This enzyme is classified as a hydrolase, and particularly acts on anester bond.

It is known that only a few percent of bacteria are present in the seaas compared to land. Acetylxylan esterase is also an enzyme possessed bymarine bacteria. For example, the marine bacteria Ochrovirga pacificaproduces acetylxylan esterase. This acetylxylan esterase is known tomaintain its activity for 120 minutes at a temperature of 45° C.(Microbial cell factories, 2019 Jul. 8 Vol. 18 issue (122)).

The present inventors have studied the use of this acetylxylan esterasefor biodegradation of cellulose acetate. In the study, it has been foundthat acetylxylan esterase is an enzyme for ester hydrolysis, and inparticular, cellulose acetate having a low substituent at 2- and3-positions is easily decomposed by acetylxylan esterase. Furthermore,it has been found that when cellulose acetate has the same total degreeof substitution, a lower degree of substitution of the substituents at2- and 3-positions is advantageous for biodegradability, particularlybiodegradability in the sea, and thereby the present disclosure has beenconceived.

From another viewpoint, it is known that the sea is weakly basic, andthat this basicity leads to deacetylation of cellulose acetate. As aresult of studies, the present inventors have found that deacetylation(hydrolysis) under basic conditions is promoted in cellulose acetate inwhich acetyl groups are heterogeneously introduced into carbon atoms at2-, 3-, and 6-positions of a glucose ring. In addition, it has beenfound that β-glucosidase is more likely to act when the glucose rings inwhich substituents at 2- and 3-positions have been hydrolyzed areconsecutive, and thereby the present disclosure has been conceived.

In the cellulose acetate of the present disclosure, at least one of thedegree of acetyl substitution at the 2-position or the degree of acetylsubstitution at the 3-position is 0.7 or less in the total degree ofacetyl substitution of 1.75 or more and 2.55 or less. In this celluloseacetate, the degrees of substitution at 2-, 3-, and 6-positions are notuniform. With the cellulose acetate of the present disclosure having alow degree of substitution of at least one of 2-position or 3-position,deacetylation under the basic conditions is promoted. It is consideredthat due to this promoting effect, the total degree of substitution ofcellulose acetate is reduced, and a high biodegradation rate in seawateris achieved.

The degrees of acetyl substitution at 2-position and 3-position are notparticularly limited as long as one of them is 0.7 or less. For example,when the degree of acetyl substitution at 2-position is 0.7 or less, thedegree of acetyl substitution at 3-position may be 1.0 or less, 0.9 orless, or 0.8 or less. Similarly, when the degree of acetyl substitutionat 3-position is 0.7 or less, the degree of acetyl substitution at2-position may be 1.0 or less, 0.9 or less, or 0.8 or less. From theviewpoint of ease of production, the degree of acetyl substitution at2-position or 3-position is preferably 0.1 or less.

Since the biodegradability in seawater is improved, at least one of thedegree of acetyl substitution at 2-position or the degree of acetylsubstitution at 3-position is preferably 0.6 or less, and morepreferably 0.5 or less. Both the degree of acetyl substitution at2-position and the degree of acetyl substitution at 3-position arepreferably 0.7 or less, more preferably 0.6 or less, and particularlypreferably 0.5 or less.

The degree of acetyl substitution at 6-position is not particularlylimited and is adjusted to satisfy the range of total degree of acetylsubstitution described below.

Each of the degrees of acetyl substitution at 2-, 3-, and 6-positions ofthe glucose ring of the cellulose acetate can be measured by NMR inaccordance with the method of Tezuka (Tezuka, Carbonydr. Res. 273, 83(1995)). That is, the free hydroxyl group of a cellulose acetate sampleis propionylated with propionic anhydride in pyridine. The resultingsample is dissolved in deuteriochloroform, and the ¹³C-NMR spectrum ismeasured. The carbon signals of the acetyl group appear in the regionfrom 169 ppm to 171 ppm in the order of 2-, 3-, and 6-positions from thehigh magnetic field; and the carbonyl carbon signals of the propionylgroup appear in the region from 172 ppm to 174 ppm in the same order.Each of the degrees of acetyl substitution at 2-, 3-, and 6-positions ofthe glucose ring in the original cellulose acetate can be determinedfrom the abundance ratio of the acetyl group and the propionyl group atrespective positions (in other words, the area ratio of the signals).The degree of acetyl substitution can be analyzed by ¹H-NMR in additionto ¹³C-NMR.

From the viewpoint of improving the biodegradability, the total degreeof acetyl substitution of the cellulose acetate is preferably 2.40 orless, and more preferably 2.20 or less. From the viewpoint of ease ofmolding, the total degree of acetyl substitution of the celluloseacetate is preferably 1.85 or more, and more preferably 2.00 or more.The total degree of acetyl substitution of the cellulose acetate may befrom 1.75 to 2.40, from 1.75 to 2.20, from 1.85 to 2.55, from 1.85 to2.40, from 1.85 to 2.20, from 2.00 to 2.55, from 2.00 to 2.40, and from2.00 to 2.20.

The total degree of acetyl substitution in the present disclosure is asum of respective degrees of acetyl substitution at the 2-, 3-, and6-positions of the glucose ring of the cellulose acetate as determinedby the measurement method described above.

[Viscosity-Average Degree of Polymerization (DPv) of Cellulose Acetate]

The viscosity-average degree of polymerization (DPv) of the celluloseacetate according to the present disclosure is not particularly limited,and is preferably 400 or less, more preferably 300 or less, still morepreferably 200 or less from the viewpoint of improving thedegradability. From the viewpoint of ease of molding, theviscosity-average degree of polymerization is preferably 10 or more,more preferably 15 or more, and particularly preferably 20 or more. Theviscosity-average degree of polymerization (DPv) may be from 10 to 400,from 10 to 300, from 10 to 200, from 15 to 40, from 15 to 300, from 15to 200, from 20 to 400, from 20 to 300, and from 20 to 200.

The viscosity-average degree of polymerization (DPv) is determined basedon the limiting viscosity number ([η] unit: cm³/g) of cellulose acetate.

The limiting viscosity number ([η], unit: cm³/g) is determined inaccordance with JIS-K-7367-1 and ISO 1628-1. Specifically, the limitingviscosity number is determined by preparing a sample solution in whichdimethyl sulfoxide (DMSO) is used as a solvent, measuring thelogarithmic relative viscosity at 25° C. using an Ubbelohde-typeviscometer of size number 1C, and dividing the logarithmic relativeviscosity at 25° C. by the concentration of the sample solution.

Using the obtained limiting viscosity number [η], the viscosity-averagemolecular weight was calculated by the following equation in accordancewith the literature of Kamide et al. (Polymer Journal, 13, 421-431(1981)).

Viscosity-average molecular weight=(limiting viscosity number[η]/0.171)(1/0.61)

Using the calculated viscosity-average molecular weight, theviscosity-average degree of polymerization (DPv) was determined by thefollowing equation.

Viscosity-average degree of polymerization (DPv)=viscosity-averagemolecular weight/(162.14+42.037×DS)

In the equation, DS is the total degree of acetyl substitution describedabove.

[Sulfuric Acid Amount in Cellulose Acetate]

From the viewpoint of improving the biodegradability in seawater, thesulfuric acid amount in the cellulose acetate of the present disclosureis preferably 10 ppm or more, and more preferably 20 ppm or more. Fromthe viewpoint of ease of production, the sulfuric acid amount ispreferably 100 ppm or less, more preferably 80 ppm or less, andparticularly preferably 50 ppm or less. The sulfuric acid amount ispreferably 10 ppm or more and 100 ppm or less, preferably 20 ppm or moreand 80 ppm or less, and particularly preferably 20 ppm or more and 50ppm or less, using 36 ppm as a median value. The sulfuric acid amount inthe cellulose acetate may be from 10 to 80 ppm, from 10 to 50 ppm, orfrom 20 to 100 ppm.

The sulfuric acid amount of the cellulose acetate is measured by thefollowing method. First, dried cellulose acetate is weighed and thenburned in an electric furnace at 1300° C., and the produced sulfurousacid gas is trapped in 10% hydrogen peroxide water. The trap liquid istitrated with a normal aqueous sodium hydroxide solution. From theobtained titration value, the sulfuric acid amount in cellulose acetateis obtained as an amount in terms of H₂SO₄ per absolute dry celluloseacetate, and the sulfuric acid amount in cellulose acetate is expressedin ppm (weight basis).

Method for Producing Cellulose Acetate

The production method of the cellulose acetate is not particularlylimited as long as the cellulose acetate has a total degree of acetylsubstitution of 1.75 or more and 2.55 or less, and at least one of thedegree of acetyl substitution at 2-position or the degree of acetylsubstitution at 3-position is 0.7 or less. The cellulose acetate of thepresent disclosure may also be obtained by hydrolyzing cellulose acetatehaving an appropriate degree of substitution and produced by a normalproducing method as a starting material.

For example, the cellulose acetate of the present disclosure is obtainedby dissolving cellulose acetate in dimethyl sulfoxide(DMSO)/water/α-amine (for example, dimethylene amine or hexamethyleneamine) and hydrolyzing the cellulose acetate. The degrees of hydrolysisat 2- and 3-positions differ depending on the type of α-amine used. Forexample, in the case of hexamethylenediamine (NH₂(CH₂)₆NH₂), the acetylgroup at the 3-position is preferentially hydrolyzed. In the case ofdimethyleneamine (HN(CH₃)₂), the acetyl group at the 2-position ispreferentially hydrolyzed.

In addition, the 2- and 3-positions are preferentially hydrolyzed byadding a sodium hydroxide/acetone/aqueous solution of about 0.1 N andheating the mixture to 40° C. to 80° C. The temperature for hydrolysisis preferably high, may be 80° C. or higher, and is preferably 100° C.or lower.

In addition, the cellulose acetate of the present disclosure may beobtained by a known method in which acetylation is performed in a statewhere a known protecting group is bonded to at least one of the carbonatom at 2-position or the carbon atom at 3-position, and thendeprotection is performed. Typically, reference is made to thetechniques disclosed in the Journal of the Japan Wood Research Society,vol 60, p 144-168 (2014), Biomacromolecules, 13, 2195-2201 (2012),Carbohydrate Polymer, 170, 23 (2017), and the like.

[Cellulose Acetate Composition]

The cellulose acetate composition according to the present disclosureincludes the cellulose acetate described above and an additive. Theadditive is selected from the group consisting of (a) to (c) below:

(a) substances of which a pH of a 1 wt. % aqueous solution at 20° C. is8 or more,

(b) substances that dissolve in water at 20° C. in an amount of 2 wt. %or more, and

(c) substances that exhibit biodegradability in seawater.

The substance (a) of which a pH of a 1 wt. % aqueous solution at 20° C.is 8 or more promotes hydrolysis (deacetylation) of cellulose acetate inweakly basic seawater. This is considered to contribute to improvementof the biodegradability of the cellulose acetate composition.

In addition, when the cellulose acetate composition is fed intoseawater, the substance (b) that dissolves in water at 20° C. in anamount of 2 wt. % or more is dissolved and eluted from the celluloseacetate composition. The substance (c) that exhibits biodegradability inseawater is gradually eluted from the cellulose acetate composition bybiodegradation from the moment when the cellulose acetate composition isfed into seawater. Due to such elution, structural voids are formed inthe molded article formed of the cellulose acetate composition, and thesubstantial surface area of the molded article is increased. It isconsidered that by increasing the surface area, the hydrolysis(deacetylation) of cellulose acetate in seawater is promoted, andmicroorganisms easily enter through voids, so that the biodegradabilityof the cellulose acetate composition is improved.

It is preferable that the action of the additive in the celluloseacetate composition is not exhibited when the cellulose acetatecomposition is used as a product, and is rapidly exhibited after thecellulose acetate composition is brought into contact with seawater.Therefore, when the additive is a solid, the additive is preferablydispersed in the cellulose acetate composition as particles, theparticle size thereof is preferably as small as possible, and thespecific surface area thereof is preferably large.

[Content of Cellulose Acetate]

From the viewpoint that high biodegradability is exhibited in seawater,the content of the cellulose acetate of the present disclosure in thecellulose acetate composition is preferably 50 wt. % or more and morepreferably 55 wt. % or more with respect to the entire composition. Thecontent of the cellulose acetate is preferably 90 wt. % or less, andmore preferably 85 wt. % or less, from the viewpoint of effectivelyexhibiting a decomposition promoting effect by the additive. The contentof the cellulose acetate in the composition of the present disclosuremay be from 50 to 90 wt. %, from 50 to 85 wt. %, from 55 to 90 wt. %,and from 55 to 85 wt. %. When two or more types of cellulose acetatewith different physical properties are used, the total amount thereof isadjusted to the aforementioned numerical range.

[Added Amount of Additive]

From the viewpoint of improving biodegradability, the total added amountof the additives in the cellulose acetate composition according to thepresent disclosure is preferably 3 wt. % or more, and more preferably 5wt. % or more, with respect to the entire composition. From theviewpoint of ease of molding, the total added amount of the additives ispreferably 40 wt. % or less and more preferably 35 wt. % or less. Thetotal added amount of the additives in the composition of the presentdisclosure may be from 3 to 40 wt. %, from 3 to 35 wt. %, from 5 to 40wt. %, and from 5 to 35 wt. %. When a plurality of additives are used,the total amount thereof is adjusted to the aforementioned numericalrange.

[Content of Cellulose Acetate and Additive]

From the viewpoint of obtaining excellent biodegradability, the totalcontent of the cellulose acetate and the additive in the celluloseacetate composition according to the present disclosure is preferably 85wt. % or more, more preferably 90 wt. % or more, and particularlypreferably 95 wt. % or more. The upper limit of the total content is notparticularly limited, and may be 100 wt. %.

[Substance (a) of Which pH of 1 wt. % Aqueous Solution at 20° C. is 8 orMore]

The substance of which a pH of a 1 wt. % aqueous solution at 20° C. is 8or more can be also referred to as a basic additive. The pH of a 1 wt. %aqueous solution of the basic additive at 20° C. is preferably 8.5 ormore and more preferably from 8.5 to 11. The pH of the 1 wt. % aqueoussolution is measured in accordance with a known procedure, and forexample, is measured with a glass pH electrode.

In the present disclosure, an “aqueous solution” does not only mean astate in which the solute is completely dissolved in water, but alsoincludes a suspension. The “suspension” includes a slurry and acolloidal solution, which are disperse systems with solid particlesdispersed in a liquid. In addition, the “1 wt. % aqueous solution” inthe present disclosure also includes those aqueous solutions for which,when the basic additive is added in water to a concentration of 1 wt. %,part of the basic additive dissolves and forms an aqueous solution, andthe remaining part of the basic additive forms a suspension.

Preferably, the substance (a) of which a pH of a 1 wt. % aqueoussolution at 20° C. is 8 or more is selected from the group consisting of(a1) to (a3) below:

(a1) inorganic compounds containing an oxygen atom bonded to any metalelement of Na, K, Ca, or Mg,

(a2) metal salts containing one or more metal ions selected from Na⁺,K⁺, Ca²⁺, or Mg²⁺, and one or more anions selected from a carbonate ion,a bicarbonate ion, a silicate ion, or an aluminate ion, and

(a3) inorganic compounds containing magnesium.

In particular, in the cellulose acetate composition containing theadditives selected from the inorganic compounds (a1) and the metal salts(a2), the seawater biodegradability is remarkably improved. It isconsidered that this is because the inorganic compounds (a1) and themetal salts (a2) exhibit basicity in seawater, thereby remarkablypromoting hydrolysis of the cellulose acetate. From this viewpoint, acomposition containing at least one type selected from (a1) and (a2) asan additive is preferable. The cellulose acetate composition of thepresent disclosure may contain, as other basic substances, basicpolymers and oligomers; basic amino acids and proteins; and basicsaccharides.

Examples of the inorganic compounds (a1) containing an oxygen atombonded to any metal element of Na, K, Ca, or Mg include oxides,hydroxides, and composite oxides of any metal element of Na, K, Ca, orMg. From the viewpoint of improving biodegradability and ease ofhandling, the inorganic compound (a1) is preferably magnesium oxide,magnesium hydroxide, talc, hydrotalcite, bentonite, calcium oxide, andcalcium hydroxide.

Examples of the metal salts (a2) containing one or more metal ionsselected from Na⁺, K⁺, Ca²⁺, or Mg²⁺, and one or more anions selectedfrom a carbonate ion, a bicarbonate ion, a silicate ion, or an aluminateion include sodium carbonate, potassium carbonate, calcium carbonate,magnesium carbonate, sodium bicarbonate, potassium bicarbonate, calciumbicarbonate, magnesium bicarbonate, calcium silicate, magnesiumsilicate, magnesium aluminate, and magnesium aluminometasilicate.

Examples of the sodium aluminate include sodium aluminum dioxide(NaAlO₂), which is a double oxide, and sodium tetrahydroxide aluminate(Na[Al(OH)₄]), which is a hydroxy complex. The magnesiumaluminometasilicate is a substance represented by the general formulaAl₂O₃.MgO.2SiO₂.xH₂O (where x represents the number of crystal water and1≤x≤10). As the magnesium aluminometasilicate, for example, magnesiumaluminometasilicate of the Japanese Pharmaceutical Codex can be suitablyused. Silicic acid is a generic term for compounds of silicon, oxygen,and hydrogen represented by the general formula[SiO_(x)(OH)_(4-2x)]_(n).

From the viewpoint of obtaining high biodegradability and excellentmoldability, preferable metal salts (a2) are calcium carbonate,magnesium carbonate, calcium silicate, magnesium silicate, magnesiumaluminate, and magnesium aluminometasilicate.

Examples of the inorganic compound (a3) containing magnesium includemagnesium oxide. The main component of the inorganic compound (a3)containing magnesium is preferably magnesium oxide.

Magnesium oxide is an oxide of magnesium represented by the chemicalformula MgO, and is also referred to as magnesia milk. Magnesium oxidemay contain a trace amount of each element of Al, Si, P, Mn, Fe, Ni, Cu,and Zn. The trace amount here means less than 1,000 ppm and preferablyless than 100 ppm.

In the present disclosure, the method for producing magnesium oxide isnot particularly limited. The method may be a method for producingmagnesium oxide by calcining and pulverizing a natural magnesiumcarbonate ore (MgCO₃) in dolomite (CaCO₃.MgCO₃), or a method forproducing magnesium oxide by precipitating magnesium ions in seawater asa hydroxide (Mg(OH)₂) and dehydrating the precipitated magnesiumhydroxide at a high temperature.

[Substance (b) that Dissolves in Water at 20° C. in Amount of 2 wt. % orMore]

The substance (b) that dissolves in water at 20° C. in amount of 2 wt. %or more may be a high molecular weight or low molecular weight materialas long as it is water-soluble. Preferably, the substance (b) thatdissolves in water at 20° C. in an amount of 2 wt. % or more is selectedfrom the group consisting of (b1) to (b3) below:

(b1) glycerin esters,

(b2) citrates, and

(b3) polyethylene glycols having a number average degree ofpolymerization of 20 or less.

The glycerin ester (b1), the citrate (b2), and the polyethylene glycol(b3) having a number average degree of polymerization of 20 or less alsoact as a plasticizer for cellulose acetate. Therefore, the celluloseacetate composition including these additives is easy to melt-mold.

The glycerin ester (b1) is a compound in which at least one hydroxylgroup of glycerin is esterified, and is a compound esterified by acarboxylic acid having preferably a molecular weight of 150 or less andmore preferably a molecular weight of 130 or less. The glycerin ester(b1) may be one in which all three hydroxyl groups of glycerin areesterified with the same carboxylic acid, one in which two hydroxylgroups are esterified with the same carboxylic acid, or one in which allthree hydroxyl groups of glycerin are esterified with differentcarboxylic acids.

The carboxylic acid may be an aliphatic carboxylic acid (fatty acid) oran aromatic carboxylic acid. From the viewpoint of reducingenvironmental load, a fatty acid is preferable. The fatty acid may be asaturated fatty acid or an unsaturated fatty acid. Preferably, theglycerin ester (b1) is esterified with a saturated fatty acid. Specificexamples of the saturated fatty acid include formic acid, acetic acid,propionic acid, butyric acid, and the like. The more preferable glycerinester (b1) is glycerin acetate having a degree of acetyl substitution of0 or more and 3 or less, and triacetin (glycerol trisacetate) in whichall three hydroxyl groups of glycerin are esterified (in other words,acetylated) with acetic acid is particularly preferable.

Triacetin is a component recognized to be safe for human intake and iseasily biodegraded, and thus has a small environmental load. Inaddition, the cellulose acetate composition formed by adding triacetinto the cellulose acetate has improved biodegradability over thecellulose acetate used alone. Furthermore, the addition of triacetin tothe cellulose acetate can efficiently lower the glass transitiontemperature of the cellulose acetate. Thus, this can impart excellentthermoformability to the raw material.

The citrate (b2) is a compound in which at least one carboxyl group ofcitric acid is esterified. The citrate (b2) may be one in which allthree carboxyl groups of citric acid are esterified with the samehydrocarbon group, one in which two carboxyl groups are esterified withthe same hydrocarbon group, or one in which all three carboxyl groups ofglycerin are esterified with different hydrocarbon groups.

The hydrocarbon group may be linear, branched, or cyclic. An aliphatichydrocarbon group is preferable, and a saturated aliphatic hydrocarbongroup (alkyl group) is more preferable. Examples of the alkyl groupinclude a methyl group, an ethyl group, and a propyl group. Examples ofthe preferable citrate (b2) include triethyl citrate and acetyl triethylcitrate.

The polyethylene glycol (b3) having a number average degree ofpolymerization of 20 or less has an ethylene oxy group as the repeatingunit. The degree of polymerization is the number of repeating units. Thepolyethylene glycol (b) having a number average degree of polymerizationof 20 or less is easily dissolved in seawater, and can contribute toimproving the biodegradability. From this viewpoint, the number averagedegree of polymerization of the polyethylene glycol is more preferably18 or less, and particularly preferably 15 or less. The number averagedegree of polymerization of the polyethylene glycol is preferably 2 ormore, and more preferably 3 or more, from the viewpoint of suppressingbleed-out in the case of a molded article. The number average degree ofpolymerization is calculated from the number average molecular weightmeasured by size exclusion chromatography (GPC) using polystyrene as astandard substance.

[Substance (c) that Exhibits Biodegradability in Seawater]

Examples of the substance (c) that exhibits biodegradability in seawaterinclude materials that undergoes degradation by not less than 50 wt. %,preferably not less than 70 wt. %, and even more preferably not lessthan 90 wt. % relative to the cellulose for comparison, after a durationof 120 days by a method specified in ASTM D6691.

Examples of the substance (c) that exhibits biodegradability in seawaterinclude polyester having a weight average molecular weight of 50,000 orless. Preference is given to polyester selected from the groupconsisting of polyhydroxybutyrate,poly(3-hydroxybutyrate-co-3-hydroxyhexanoate, polybutylene succinate,polycaprolactone, and polyglycolic acid.

[Combinations of Preferable Additives]

From the viewpoint of improving biodegradability, the cellulose acetatecomposition of the present disclosure preferably includes an additiveselected from magnesium oxide, magnesium aluminometasilicate, andtriacetin. From the viewpoint of improving biodegradability and ease ofmolding, the cellulose acetate composition of the present disclosurepreferably includes at least one selected from magnesium oxide andmagnesium aluminometasilicate, and triacetin. An additive including acombination of magnesium oxide and triacetin is more preferable.

[Method for Producing Cellulose Acetate Composition]

The cellulose acetate composition of the present disclosure is obtainedby mixing cellulose acetate having a total degree of acetyl substitutionof 1.75 or more and 2.55 or less, in which at least one of the degree ofacetyl substitution at 2-position or the degree of acetyl substitutionat 3-position is 0.7 or less, and the above-described additive in asolvent such as acetone, and then removing the solvent. The celluloseacetate composition of the present disclosure may be obtained bymelt-kneading. Preferably, the composition is obtained by mixing thecellulose acetate and the additive, and then melt-kneading. By mixingbefore melt-kneading, the additive and the cellulose acetate are moreuniformly mixed with each other in a short time to homogenize theresulting kneaded product, so that a composition with improved meltfluidity and processing accuracy is obtained.

A known mixer such as a Henschel mixer can be used for mixing thecellulose acetate and the additive. Dry mixing or wet mixing may beused. In using a mixer such as a Henschel mixer, the temperature in themixer is preferably a temperature at which the cellulose acetate doesnot melt, for example, in a range of not lower than 20° C. and lowerthan 200° C.

An extruder such as a twin-screw extruder can be used for melt-kneadingthe cellulose acetate and the additive or melt-kneading after mixing thecellulose acetate and the additive. From the viewpoint of uniformity ofthe kneaded product and suppression of degradation due to heating, thekneading temperature (cylinder temperature) of the extruder ispreferably 170° C. or higher and 230° C. or lower. For example, whenmelt-kneading is performed using a twin-screw extruder, the kneadingtemperature (also referred to as cylinder temperature) may be 200° C.The kneaded product may be extruded into a strand shape from a dieattached to the tip of the twin-screw extruder and then hot-cut intopellets. Here, the die temperature may be approximately 220° C.

The added amount of the additive to the entire cellulose acetatecomposition obtained is preferably 3 wt. % or more and 40 wt. % or less.When two or more kinds of additives are blended, the total amountthereof is adjusted to 3 wt. % or more and 40 wt. % or less.

The blending amount of the cellulose acetate with respect to the entirecellulose acetate composition obtained is preferably 50 wt. % or more,and more preferably 50 wt. % or more and 90 wt. % or less. When two ormore kinds of cellulose acetate are blended, the total amount thereof isadjusted to preferably 50 wt. % or more, and more preferably 50 wt. % ormore and 90 wt. % or less.

In the range that does not inhibit the biodegradability of the celluloseacetate composition, other additives that are different from theadditives described above may be blended in this composition. Examplesof other additives include colorants, ultraviolet absorbers, lightstabilizers, antioxidants, thermal stabilizers, optical characteristicmodifiers, fluorescent brighteners, and flame retardants. In this case,the total content of the cellulose acetate and the additive in thecellulose acetate composition is preferably 85 wt. % or more.

The cellulose acetate of the present disclosure has excellent meltmoldability and is thus suitable for melt molding. The form of themolded article formed by molding the cellulose acetate composition ofthe present disclosure is not particularly limited, and examples includea one-dimensional molded article, such as fibers; a two-dimensionalmolded article, such as films; and a three-dimensional molded article,such as particles including pellets, tubes, and hollow cylindricalshapes.

The cellulose acetate or the cellulose acetate composition of thepresent disclosure has excellent biodegradability in seawater and isthus suitable for products often disposed, including straws, containerssuch as cups, packaging materials, binders, and tobacco filters; fibersfor clothing; nonwoven fabrics; products at least partially flowing withwater into the environment during use, such as cosmetic beads andscrubs; and products expected to be flushed into a toilet, such ashygiene materials (diapers and sanitary products).

EXAMPLES

Hereinafter, effects of the present disclosure will be appreciated byexamples. Note that each of the configurations, combinations thereof,and the like in each of the embodiments are an example, and variousadditions, omissions, substitutions, and other changes may be made asappropriate without departing from the spirit of the present disclosure.The present disclosure is not limited by the embodiments and is limitedonly by the claims. Unless otherwise specified, all test temperaturesare room temperature (20° C.±5° C.).

Example 1

Cellulose acetate of Example 1 was synthesized with reference to theJournal of the Japan Wood Research Society, vol 60, p 144-168 (2014),and Biomacromolecules, 13, 2195-2201 (2012).

First, 100.4 g of cellulose (linter raw material) was added to 3 L of anaqueous NaOH solution having a concentration of 18 wt. %, and themixture was stirred at room temperature for 1 hour. Thereafter, thecellulose was collected by filtration and washed with water until thewashing solution became neutral. Next, this cellulose was added to 500ml of dimethylacetamide, and the mixture was stirred at room temperaturefor 12 hours. Thereafter, the cellulose removed by filtration was washedtwice with 500 mL of dimethylacetamide.

Subsequently, this cellulose was added to 4 L of dimethylacetamide,heated at 150° C. for 1 hour, and then cooled until the liquidtemperature reached 100° C. Thereafter, 350 g of anhydrous lithiumchloride was added, and the mixture was stirred at 100° C. for 1 hourand cooled to 25° C. to dissolve the cellulose in a lithiumchloride/dimethylacetamide (DMAC)-based solvent.

To the obtained cellulose solution, 200 g of imidazole and 450 g ofthexyldimethyl silyl chloride (1,1,2-trimethylpropyl dimethyl silylchloride) were added and reacted, and cellulose in which the 2- and6-positions are silyl etherified was obtained. This crude product waswashed with 1.5 L of methanol three times, and 268.0 g of 2,6 silyletherified cellulose was obtained.

265.5 g of the obtained 2,6 silyl etherified cellulose was dissolved in2,000 g of dimethylacetamide and 165.9 g of pyridine and then reactedwith 142.2 g of allyl chloride. The obtained reaction solution was addedto methanol to precipitate, the precipitate (crude product) was washedthree times with 1.0 L of methanol, and 265.5 g of a product wasobtained. This product was dissolved in 4,000 g of dimethylacetamide andreacted with 380 g of tetrabutylammonium fluoride, and 77.7 g ofcellulose in which the 3-position is allyl etherified was obtained.

77.7 g of the obtained 3 allyl cellulose was dissolved in 800 g ofdimethylacetamide, 167 g of acetic anhydride and 136 g of pyridine wereadded thereto and reacted, and 2,6-acetyl-3 allyl cellulose wasobtained. Thereafter, 4.9 g of tetrakis(tri-phenylphosphine)palladiumwas further added to isomerize an allyl ether group, and the resultingmixture was reacted with K₂CO₃ to deprotect the allyl group, therebyobtaining 73.2 g of cellulose acetate of Example 1 in which the 2- and6-positions were selectively substituted. The free hydroxyl groups ofcellulose acetate were propionylated by the method described above, andthe degree of substitution at the 2-, 3-, and 6-positions was determinedby measuring a ¹³C-NMR spectrum in deuterated chloroform. The resultsobtained are shown in Table 1 below as DS2, DS3, and DS6, respectively.The total degree of acetyl substitution is the sum of the degrees ofacetyl substitution at the 2-, 3-, and 6-positions. The celluloseacetate of Example 1 had a DS2 of 0.98, a DS3 of 0.47, and a DS6 of1.00, and the total degree of acetyl substitution was 2.45.

After 10 parts by weight of the cellulose acetate obtained in Example 1was heated at 110° C. for 2 hours and dried, the cellulose acetate wascharged into 90 parts by weight of acetone, stirred at 25° C. for 6hours, and dissolved, thereby preparing a dope for film production. Thisdope was allowed to flow on a glass plate, casted with a bar coater, anddried at 40° C. for 30 minutes. Then, the film was peeled off from theglass plate, dried at 80° C. for another 30 minutes, thereby obtaining acellulose acetate film (thickness of 30 μm) of Example 1.

Example 2

Cellulose acetate of Example 2 was synthesized with reference to JP2015-224256 A.

First, 50 g of cellulose acetate (degree of acetyl substitution: 2.87)was dissolved in 500 g of N-methylpyrrolidone. Next, 57 g of cesiumcarbonate was added and stirred at room temperature for 10 hours to bereacted. The resulting reaction solution was precipitated by addition ofan appropriate amount of water, and the precipitate was washed withmethanol and dried, and 37.8 g of cellulose acetate in Example 2 wasobtained. The degrees of substitution at the 2-, 3-, and 6-positionswere determined by measuring ¹H-NMR spectrum in the same manner as inExample 1. The obtained results are shown in Table 1 below. Thecellulose acetate of Example 2 had a DS2 of 0.65, a DS3 of 0.75, and aDS6 of 0.83, and the total degree of acetyl substitution was 2.23.

Using the obtained cellulose acetate, a cellulose acetate film(thickness: 30 μm) of Example 2 was obtained in the same manner as inExample 1.

Example 3

First, 4.5 g of cellulose from a linter pulp was dissolved in 75 g of1-butyl-3-methylimidazolium chloride. Next, acetic anhydride was addedin an amount of 4.9 mol times (13.8 g) with respect to a celluloseskeleton, and the mixture was reacted at 80° C. for 1 hour. Thereafter,the resulting reaction solution was precipitated by addition of anappropriate amount of methanol, and the precipitate was washed withmethanol and dried, and 5.44 g of cellulose acetate in Example 3 wasobtained. The degrees of substitution at the 2-, 3-, and 6-positionswere determined by measuring ¹H-NMR spectrum in the same manner as inExample 1. The obtained results are shown in Table 1 below. Thecellulose acetate of Example 3 had a DS2 of 0.49, a DS3 of 0.66, and aDS6 of 0.95, and the total degree of acetyl substitution was 2.10.

Using the obtained cellulose acetate, a cellulose acetate film(thickness: 30 μm) of Example 3 was obtained in the same manner as inExample 1.

Example 4

Cellulose acetate of Example 1 was synthesized with reference to theJournal of the Japan Wood Research Society, vol 60, p 144-168 (2014),and Biomacromolecules, 13, 2195-2201 (2012).

First, 100.4 g of cellulose as previously described in Examples 1 to 3was added to 3 L of an aqueous NaOH solution having a concentration of18 wt. %, and the mixture was stirred at room temperature for 1 hour.Thereafter, the solid content (alkali cellulose) was collected byfiltration and washed with water until the washing solution becameneutral. Next, this cellulose was added to 500 ml of dimethylacetamide,and the mixture was stirred at room temperature for 12 hours.Thereafter, the cellulose removed by filtration was washed twice with500 mL of dimethylacetamide.

Subsequently, this cellulose was added to 4 L of dimethylacetamide,heated at 150° C. for 1 hour, and then cooled until the liquidtemperature reached 100° C. Thereafter, 350 g of anhydrous lithiumchloride was added, and the mixture was stirred at 100° C. for 1 hourand cooled to 25° C. to dissolve the cellulose in a lithiumchloride/dimethylacetamide (DMAC)-based solvent.

To the obtained cellulose solution, 200 g of imidazole and 237.2 g ofthexyldimethyl silyl chloride (1,1,2-trimethylpropyl dimethyl silylchloride) were added and reacted, and cellulose in which the 2- and6-positions are silyl etherified was obtained. This crude product waswashed with 1.5 L of methanol three times, and 168.0 g of 2,6 silyletherified cellulose was obtained.

The total amount of the obtained 2,6 silyl etherified cellulose wasdissolved in 800 g of dimethylacetamide, and 387.6 g of acetic anhydrideand 316. g of pyridine were added and reacted to acetylate the remaininghydroxyl groups. 1.5 L of methanol was added to the obtained reactionsolution, thereby obtaining a precipitate. This precipitate wascollected by filtration and then washed 3 times with 500 mL of methanol,and 203 g of a product was obtained.

The obtained product was dissolved in 4 L of dimethyl sulfoxide, andreacted with 469 g of tetrabutylammonium fluoride to deprotect a silylether group, thereby obtaining 82.4 g of cellulose acetate of Example 4.The degrees of substitution at the 2-, 3-, and 6-positions weredetermined by measuring ¹H-NMR spectrum in the same manner as inExample 1. The obtained results are shown in Table 1 below. Thecellulose acetate of Example 4 had a DS2 of 0.42, a DS3 of 1.00, and aDS6 of 0.46, and the total degree of acetyl substitution was 1.88.

Using the obtained cellulose acetate, a cellulose acetate film(thickness: 30 μm) of Example 4 was obtained in the same manner as inExample 1.

Comparative Example 1

A hardwood prehydrolysis kraft pulp with an a-cellulose content of 98.4wt. % was ground with a disc refiner into a cotton-like form. Onto 100parts by weight of the ground pulp (water content percentage of 8%),26.8 parts by weight of acetic acid was sprayed. The mixture wasthoroughly stirred and then pretreated by allowing the mixture to standfor 60 hours to be activated. The activated pulp was added to a mixtureof 323 parts by weight of acetic acid, 245 parts by weight of aceticanhydride, and 13.1 parts by weight of sulfuric acid. The temperaturewas adjusted from 5° C. to a maximum temperature of 40° C. over 40minutes, and the pulp was acetylated for 90 minutes. A neutralizingagent (24% aqueous solution of magnesium acetate) was added over 3minutes, and thus the sulfuric acid amount (sulfuric acid amount foraging) was adjusted to 2.5 parts by weight. Furthermore, the temperatureof the reaction bath was raised to 75° C., then water was added, and thewater content in the reaction bath (water content for aging) wasadjusted to a concentration of 52 mol %. The water concentration foraging was expressed in mol % by multiplying the proportion expressed inmolar ratio of the water content in the reaction bath to acetic acid by100. Then, aging was performed at 85° C. for 100 minutes, magnesiumacetate was added to neutralize sulfuric acid to terminate the aging,and a reaction mixture containing cellulose acetate was obtained. Adilute aqueous solution of acetic acid was added to the resultingreaction mixture. The cellulose acetate was separated, then washed,dried, and stabilized with calcium hydroxide, and the cellulose acetateof Comparative Example 1 was obtained.

The degrees of substitution at the 2-, 3-, and 6-positions weredetermined by measuring ¹³C-NMR spectrum in the same manner as inExample 1. The obtained results are shown in Table 1 below. Thecellulose acetate of Comparative Example 1 had a DS2 of 0.86, a DS3 of0.85, and a DS6 of 0.75, and the total degree of acetyl substitution was2.46.

Using the obtained cellulose acetate, a cellulose acetate film(thickness: 30 μm) of Comparative Example 1 was obtained in the samemanner as in Example 1.

Examples 5, 10, 15, and 20

After 9.5 parts by weight of the cellulose acetate in each of Examples 1to 4 was heated at 110° C. for 2 hours and dried, the cellulose acetatewas charged into 90 parts by weight of acetone, stirred at 25° C. for 6hours, and dissolved. To this mixed solution, 0.5 parts by weight of apowder of magnesium aluminometasilicate was added as an additive. Themixture was further stirred at 25° C. for 6 hours, and a dope for filmproduction was prepared. This dope was allowed to flow on a glass plateand casted with a bar coater, and dried at 40° C. for 30 minutes. Then,the film was peeled off from the glass plate, dried at 80° C. foranother 30 minutes, and cellulose acetate composition films (thicknessof 30 μm) of Examples 5, 10, 15, and 20 were obtained.

Examples 6, 11, 16, and 21

Cellulose acetate composition films (thickness: 30 μm) of Examples 6,11, 16, and 21 were obtained in the same manner as in Examples 5, 10,15, and 20 except that magnesium oxide was used as an additive, and theadditive was added in an amount of 0.4 parts by weight with respect to9.6 parts by weight of each cellulose acetate.

Examples 7, 12, 17, and 22

Cellulose acetate composition films (thickness: 30 μm) of Examples 7,12, 17, and 22 were obtained in the same manner as in Examples 5, 10,15, and 20 except that triacetin was used as an additive, and theadditive was added in an amount of 2.0 parts by weight with respect to8.0 parts by weight of each cellulose acetate.

Examples 8, 13, 18, and 23

Cellulose acetate composition films (thickness 30 μm) of Examples 8, 13,18, and 23 were obtained in the same manner as in Examples 5, 10, 15,and 20 except that magnesium aluminometasilicate and triacetin were usedas additives, and 0.5 parts by weight of magnesium aluminometasilicateand 2.0 parts by weight of triacetin were added with respect to 7.5parts by weight of each cellulose acetate.

Examples 9, 14, 19, and 24

Cellulose acetate composition films (thickness 30 μm) of Examples 9, 14,19, and 24 were obtained in the same manner as in Examples 5, 10, 15,and 20 except that magnesium oxide and triacetin were used as additives,and 0.4 parts by weight of magnesium oxide and 2.0 parts by weight oftriacetin were added with respect to 7.6 parts by weight of eachcellulose acetate.

[Evaluation of Degree of Seawater Biodegradation]

According to the following procedure, each of the cellulose acetatefilms of Examples 1 to 4 and Comparative Example 1 and the celluloseacetate composition films of Examples 5 to 24 were pulverized to anaverage particle size of about 20 um, and then subjected to thefollowing biodegradation test.

60 mg of each sample was charged into 250 g of seawater, and stirred ata temperature of 30° C. The amount of carbon dioxide generated wasmeasured 90 days and 120 days after the sample was charged. Thetheoretical carbon dioxide generation amount was calculated from thetotal organic carbon amount (TOC) measured for each sample subjected tothe test, and the ratio of the value obtained by subtracting themeasured value of the blank (seawater only) from the measured value tothe theoretical carbon dioxide generation amount was taken as the degreeof biodegradation (%). The obtained results are shown in Tables 1 and 2below.

TABLE 1 Biodegradability Total Degree of degree biodegradation [wt. %]of acetyl 0 90 120 substitution DS2 DS3 DS6 days days days Example 12.45 0.98 0.47 1.00 0 34.4 62.0 Example 2 2.23 0.65 0.75 0.83 0 49.176.0 Example 3 2.10 0.49 0.66 0.95 0 53.3 83.5 Example 4 1.88 0.42 1.000.46 0 75.7 91.5 Comparative 2.46 0.86 0.85 0.75 0 26.3 54.0 Example 1

TABLE 2 Biodegradability Total Degree of degree Additive biodegradation[wt. %] of acetyl Content 0 90 120 substitution DS2 DS3 DS6 Type (wt. %)days days days Example 5 2.45 0.98 0.47 1.00 Mg aluminometasilicate 5 044.6 72.9 Example 6 2.45 0.98 0.47 1.00 MgO 4 0 44.0 72.3 Example 7 2.450.98 0.47 1.00 Triacetin 20 0 54.4 82.3 Example 8 2.45 0.98 0.47 1.00 Mgaluminometasilicate 5 0 63.7 92.7 Triacetin 20 Example 9 2.45 0.98 0.471.00 MgO 4 0 63.5 92.1 Triacetin 20 Example 10 2.23 0.65 0.75 0.83 Mgaluminometasilicate 5 0 66.4 94.1 Example 11 2.23 0.65 0.75 0.83 MgO 4 066.2 93.6 Example 12 2.23 0.65 0.75 0.83 Triacetin 20 0 71.0 97.0Example 13 2.23 0.65 0.75 0.83 Mg aluminometasilicate 5 0 86.0 96.0Triacetin 20 Example 14 2.23 0.65 0.75 0.83 MgO 4 0 86.3 96.2 Triacetin20 Example 15 2.10 0.49 0.66 0.95 Mg aluminometasilicate 5 0 69.3 97.4Example 16 2.10 0.49 0.66 0.95 MgO 4 0 69.0 98.0 Example 17 2.10 0.490.66 0.95 Triacetin 20 0 73.3 98.4 Example 18 2.10 0.49 0.66 0.95 Mgaluminometasilicate 5 0 89.3 96.8 Triacetin 20 Example 19 2.10 0.49 0.660.95 MgO 4 0 88.8 98.8 Triacetin 20 Example 20 1.88 0.42 1.00 0.46 Mgaluminometasilicate 5 0 98.8 99.0 Example 21 1.88 0.42 1.00 0.46 MgO 4 098.3 98.9 Example 22 1.88 0.42 1.00 0.46 Triacetin 20 0 96.1 98.7Example 23 1.88 0.42 1.00 0.46 Mg aluminometasilicate 5 0 96.3 97.7Triacetin 20 Example 24 1.88 0.42 1.00 0.46 MgO 4 0 97.4 97.8 Triacetin20

As shown in Tables 1 and 2, the cellulose acetates of Examples have ahigher decomposition rate in seawater than that of cellulose acetates ofComparative Examples. In addition, the cellulose acetate compositions ofExamples contained additives, thereby improving the decomposition ratein seawater as compared with the corresponding cellulose acetates. Fromthis evaluation result, the superiority of the present disclosure isclear.

INDUSTRIAL APPLICABILITY

The cellulose acetate and the composition described above are notlimited to the film shape, and can be applied as biodegradable moldedarticles in various shapes.

1. A method of producing cellulose acetate, comprising: hydrolyzing astarting cellulose acetate to produce the cellulose acetate, wherein thecellulose acetate has a total degree of acetyl substitution of 1.75 ormore and 2.55 or less, and a degree of acetyl substitution at 2-positionor a degree of acetyl substitution at 3-position of the celluloseacetate is 0.7 or less and 0.42 or more.
 2. The method of claim 1,wherein the degree of acetyl substitution at 2-position and the degreeof acetyl substitution at 3-position of the cellulose acetate each are0.7 or less.
 3. The method of claim 1, wherein the total degree ofacetyl substitution of the cellulose acetate is 2.00 or more.
 4. Themethod of claim 1, wherein the total degree of acetyl substitution ofthe cellulose acetate is 2.20 or less.
 5. The method of claim 1, whereina degree of acetyl substitution at 6-position of the ceullulose acetateis 0.83 or more and 1.00 or less.
 6. The method of claim 1, wherein adegree of acetyl substitution at 6-position of the cellulose acetate is0.83 or more and 1.00 or less and the total degree of acetylsubstitution of the cellulose acetate is 2.00 or more and 2.55 or less.7. The method of claim 1, wherein the hydrolyzing the starting celluloseacetate comprises dissolving the starting cellulose acetate in dimethylsulfoxide/water/α-amine to form a mixture and hydrolyzing the startingcellulsoe acetate in the mixture.
 8. The method of claim 7, wherein thea-amine is dimethylene amine
 9. The method of claim 7, wherein thea-amine is hexamethylene diamine.
 10. The method of claim 7, wherein thehydrolyzing the starting cellulose acetate further comprises addingsodium hydroxide/acetone/aqueous solution in the mixture and heating themixture to a range of 40° C. to 80° C.
 11. A method of producing acellulose acetate composition, comprising: mixing the celluslose acetateaccording to claim 1 with an additive, wherein the additive comprises atleast one selected from the group consisting of (a) substances of whicha pH of a 1 wt. % aqueous solution at 20° C. is 8 or more, (b)substances that dissolve in water at 20° C. in an amount of 2 wt. % ormore, and (c) substances that exhibit biodegradability in seawater. 12.The method of claim 11, wherein a content of the cellulose acetate is 50wt. % or more of the cellulose acetate composition.
 13. The method ofclaim 11, wherein a total content of the additive is 3 wt. % or more and40 wt. % or less of the cellulose acetate composition.
 14. The method ofclaim 11, wherein the additive comprises at least one selected from (a)substances of which a pH of a 1 wt. % aqueous solution at 20° C. is 8 ormore, which are selected from the group consisting of (a1) inorganiccompounds containing an oxygen atom bonded to any metal element of Na,K, Ca, or Mg, (a2) metal salts containing one or more metal ionsselected from Na⁺, K⁺, Ca²⁺, or Mg²⁺, and one or more anions selectedfrom a carbonate ion, a bicarbonate ion, a silicate ion, or an aluminateion, and (a3) inorganic compounds containing magnesium.
 15. The methodof claim 14, wherein the additive comprises at least one selected from(a3) inorganic compounds containing magnesium, which comprise magnesiumoxide as an main component.
 16. The method of claim 11, wherein theadditive comprises at least one selected from (b) substances thatdissolve in water at 20° C. in an amount of 2 wt. % or more, which areselected from the group consisting of (b1) glycerin esters, (b2)citrates, and (b3) polyethylene glycols having a number average degreeof polymerization of 20 or less.
 17. The method of claim 11, wherein theadditive comprises at least one selected from (c) substances thatexhibit biodegradability in seawater, which are polyesters having aweight average molecular weight of 50,000 or less.
 18. The method ofclaim 11, wherein the additive comprises a combination of magnesiumoxide and triacetin.
 19. A method of producing a cellulose acetate,comprising: performing acetylation of a celullose wherein a protectiongroup is bonded to at least one of a carbon atom of the cellulose at2-position or a carbon atom at 3 -position, and performing deprotectionof the protection group bonded at the at least one of the carbon atom ofthe cellulose at 2-position or the carbon atom at 3 -position to obtainthe cellulose acetate, wherein the cellulose acetate has a total degreeof acetyl substitution of 1.75 or more and 2.55 or less, and a degree ofacetyl substitution at 2-position or a degree of acetyl substitution at3-position of the cellulose acetate is 0.7 or less and 0.42 or more. 20.The method of claim 19, wherein the protecton group is a chloride group.